The sunken sewer is a quite small irradiated underground location, containing some feral ghouls and possibly a glowing one or feral ghoul reaver (with the Broken Steel add-on). It can be reached from the northern part of Dupont Circle. It is more strongly radioactive than most of the sewers, and players should take that into account if they wish to enter.

On entering the area, the first thing to notice is the very high level of background radiation - up to 20 rads/sec without Radiation Resistance modifiers. The ladder is at the end of a short sewer section which joins from the East to a small room with catwalk over a cavern filled to the top with radiation barrels. There is a safe on the northern side adjacent to a couple of shelves which contain the loot for this small area.